EP 1 322 265 B1 describes a foot insert for an artificial foot, with an upper, approximately roof-shaped spring having, in the roof top area, an adapter attachment and, starting from the latter, a heel spring which extends downward in a concave curve into the heel area, and a forefoot spring which extends downward in a concave curve into the forefoot area. A base spring is connected to the free branch ends of the heel spring and of the forefoot spring, such that a spring deflection space is formed. In terms of dimensional elasticity and flexural elasticity, the base spring and the forefoot spring are configured in such a way that, under the effect of an increasing load in the forefoot area, the forefoot spring and the base spring successively bear against each other in this area. A prosthetic foot insert of this kind has good service properties, but it places high demands on the material to be used.
EP 1 357 867 B1 describes a below-knee prosthesis with an upper foot plate, and a forefoot plate and heel plate arranged below the latter and connected to the upper foot plate via an intermediate elastomeric layer, wherein the intermediate elastomeric layer holds the forefoot plate and the heel plate at a distance from each other. The gap between the forefoot plate and the heel plate is located in a middle foot portion and ensures that the plates are able to move independently of each other.
Moreover, a prosthetic foot insert with a continuous upper spring and a divided lower spring is known from the company Otto Bock. The front area of the lower spring and the rear area of the lower spring are separate from each other and are secured on the upper spring via a continuous elastomeric element. The heel compliance is produced by the elastomeric join, the forefoot compliance from the cooperation between the upper spring, the lower springs and the elastomeric element.
A further model of a prosthetic foot insert from the company Otto Bock has a continuous upper spring and a continuous lower spring, which have a continuous elastomeric join. The heel compliance is produced by the rear part of the lower spring and by the elastomeric element, the compliance in the forefoot area from the upper and lower springs and the elastomeric element. A prosthetic foot insert of this kind has a low structural height but, for this reason, also a stiff forefoot. The heel function is relatively soft and, as a result of a short free spring length, has a considerable progression.
In passive prosthetic feet, a compromise is made between standing properties and walking properties, since they lack the possibility of a muscular compensation. For improved stability when standing, feet are therefore produced with a rigid forefoot lever, whereas feet for better walking properties have softer forefoot levers. On the basis of measured values, active prosthetic feet are able to decide which activity is ongoing and can accordingly modify the properties and adjust themselves to the particular activity.